Electric tank heater control system



Oct. 16, 1945. c. M. OSTERHELD 2,387,180

ELECTRIC TANK HEATER CONTROL SYSTEM Filed July 20 1944 INVENZTOR. CL AR/ Gamma BY l ATTORNEY Patented Oct. 16, 1945 ELECTRIC TANK HEATER CONTROL SYSTEM Clark M. Osterheld,

McGraw Electric Stoughton, Wis., assignor to Company, Elgin, Ill., poration of Delaware Application July 20, 1944, Serial No. 545,766

4 Claims.

My invention relates to electric heating and particularly to control systems for electric heaters of domestic hot water tanks.

Among the objects of my invention are the following: to provide a control system that shall effect immediate energization of the electric heat er of a hot water tank after closing of a timecontrolled switch at the start of an off-peak period in case a relatively large amount of hot water has been withdrawn from the tank during an onpeak period; that shall effect energization of the heater after closing of the time-controlled switch at the start of an off-peak period with a predetermined time period of delay in case a relatively small amount of hot water has been Withdrawn from the tank during the on-peak period; and that shall continue energization of the heater, if necessary, until substantially all of the water in the tank has been heated to a predetermined high temperature, irrespective of the opening of the time-controlled switch at the end of an off-peak period.

In the drawing,

Figure 1 is a view in vertical section through an ordinary domestic hot water tank, having associated therewith a control system embodying my invention, and,

Fig. 2 is a diagram of connections embodying my invention.

Referring first of all to Fig. 1 of the drawing, I have there shown an ordinary domestic hot Water tank II, having a lower cold water inlet pipe I3, an upper hot water outlet pipe I5, and being surrounded by a mass I I of heat insulation, which heat insulation is held in proper operative position around the tank I I by an outer casing I9.

I provide preferably, but not necessarily, a sin gle electric heater 2|, which may be of the clampon type and which is located around the bottom end portion of tank I I in a tunnel 23. It may be here pointed out that all of the above mentioned details form no part of my present invention and are all well known in the art.

I provide a lower thermally-actuable heater control switch, designated by numeral 25, and I have shown this as including a tubular member 21, having a closed inner end and having its outer open end secured in an opening in tank II in a fluid-tight manner. An expansion rod 29 is located in tube 21 and is adapted to have its outer end engaged with and be disengaged from a block 3| of electric-insulating material mounted on the outer free end of a contact arm 33, which is of substantially resilient construction and has located thereon a contact member adapted to engage with and be disengaged from a cooperating contact member on a substantially rigid contact arm 35. The two contact arms are supported on tank II as by blocks 31 of electric-insulating material. The design, construction, and adjustment of the thermally-actuable heater control switch 35 is such that when tube 21 is surrounded by cold water, the length of expansion rod 29 will be such that it will be out of engagement with electric-insulating block 3|, so that the two contact arms 33 and 35 will be in electric-conducting engagement with each other. When tube 21 is surrounded by hot water, the length of expansion rod 29 will be such that the contact on contact arm 33 will be out of engagement with the contact on contact arm 35. When I speak of cold water, I mean water, the temperature of which is on the order of to F., or thereabouts; and when I speak of hot water, I mean water, the temperature of which is on the order of F., or slightly higher.

Referring now particularly to Fig. 2 of the drawing, I have there shown a diagram of connections embodying a particular construction of thermal retarder, which is designated generally by numeral 39. The thermal retarder 39 is preferably located in heat-receiving relation on a tank at substantially the mid-height thereof. It includes a first thermal switch which is normally closed when subject to cold water and a second thermal switch which is normally open when subject to the temperature of cold and of hot Water in the tank and is closed when its temperature is appreciably above that of hot water, say on the order of 250 F. or more. The general details of construction of the thermal retarder heater control switch unit 39 are shown in my copending application, S. N. 537,941, filed May 29, 1944, and assigned to the same assignee as is the present application.

The thermal retarder switch unit includes a first switch, having a bimetal bar II, which has insulatedly mounted thereon a contact bridgin member 43 adapted to engage with and be disengaged from two fixed contacts 45 and 41. A second bimetal bar 5| has mounted thereon at one end thereof a pair of pivot plates 49 which are adapted to be pivotally engaged by the sharpened ends of the first bimetal bar 4|. The bimetal bars 4| and 5| are the two toggle arms of a snapacting mechanism comprising an over center spring 53 located in aligned slots in the adjacent ends of the two bimetal bars. The outer end of the second bimetal bar 5| is rigidly supported. When bridging member 43 moves with a snap action to open position, it will engage a stop member 54.

The second thermal snap-acting switch of the thermal retarder unit 39 includes a first bimetal bar 55 having mounted on one end thereof a contact bridging member 51 with suitable electric insulation therebetween. A econd bimetal bar 59 has one end fixedlysupported'and is provided at its other end with a pair of pivot plates49, which are adapted to be pivotally engaged by the sharpened ends of the first bimetal bar 55, and an over center spring BI is positioned in two aligned slots in the adjacent ends of bimetal bars 55 and 59. The contact bridging member 51 is adapted to engage with and be disengaged from three fixed contacts 63, 65, and 61 and will engage a stop member 68 when moved with a snap action to open position. While I have shown the contacts 63, 65, and 61 generally only, it is to be understood that any means for insuring proper contact pressure betweenthese contacts and the contact bridging member will be employed in a manner well known in the art.

The design, construction, and adjustment of.

the first thermal retarder switch is such that the contact bridging member will be in engagement with fixed contacts 45 and 41 when subject to cold water in the tank and will be disengaged therefrom when subject to hot water in the tank. The second thermal switch of the thermal retarder switch unit, comprising particularly the bimetal bars 55' and 59, is so designed, constructed, and adjusted that the bridging member 51 will be out of. engagement with the fixed contact members.63-, 65-, and 61 when subject to cold and to.

hot water in the tank and will be in engagement therewith when subject to a higher temperature, on the order of 250 F. or over. In orderto obtain this appreciably higher. temperature, I provide a heating coil 69, which may be insulatedly mounted on and supported by bimetal bar 55; In order to obtain the hereinbefore described operation, I may use. heavier bimetal bars or bimetal bars which'are not ashighly thermally-responsive asare the bars 4| and 5|.

I provide further a time-controlled switch, designated generally by numeral?! and including apair of contact'arm's 'lfi and which are adapted to be held in engaging and electric-conducting position relatively to each other during oil-peak periods of a twenty-four hour day by any continuously operative timing means now well known in the'art. The contact arms 13 and 15 will be out ofengagement'with each other during all onpeak-periods of a twenty-four hour day.

I provide a first supply circuit conductor H and asecond supply circuit conductor 19; The first supply circuit conductor 11 is connected to contact arm 13, and the second contact arm 15 is connected by a conductor 8| with the" first contact 45 of the first thermal retarder switch. The two' fixed contacts and 63 are connected by a conductor 83, which conductor is connected by a conductor85 with one terminal of the heater 2 the otheriterminal of which is connected'by a conductor iilwith'contact' arm 35 of the lower thermally-actuable switch 25. The other contact1arm33'of switch 25 is connected to the other supply'circ'uit conductor 79 by a conductor 89. Contact 65is connected by a conductor 9| with conductor 8| and by a conductor 99 with one terminal of heating coil 69, the other terminal of which-is connected by a conductor 95 with contact arm135. The third fixed contact 61 of the secondthermal retarder switch is connected by a conductor 91 with contact arm 73 and the first supply circuit conductor 71.

The design, construction, and adjustment of heating coil 59 insulatedly mounted on bimetal bar 55 is such that the relatively low-wattage translated therein into heat will cause temperature rise of bimetal bar 55 to a value on the order of 250 F. in say from four to six hours, and if desired, I may provide any means well known in the art to vary the watts translated into heat in heating coil 69, such as an adjustable rheostat.

Let it now be assumed that the system operated, as will be hereinafter described in detail, so that at the end of the off-peak period, during the late night hours and ending say at 6 a. m., the tank was full of hot Water. Let it be further assumed that during normal use of hot water during the day, withdrawals of hot water from the tank were such as to cause the thermal retarder switch unit to be subject to cold water and contact bridging member 43 to be in engagement with fixed contacts 45 and 41 at say 10 p. m., which, for illustrative purposes, may be considered to be the start of the off-peak period, running through the late night hours. The closure of the time-controlled switch H at 10 p, m, will therefore cause immediate energization of heater 2| through a circuit substantially as follows: from supply circuit conductor 11 through engaged contact arms 13 and 15, conductor 8 through the engaged contacts 45 and 4! with bridging member 43, through a part of conductor 83, then through conductor-B5 and heater 2|, through conductor 81, then through the engaged contact arms and 33 and through conductor 89 to the second supply circuit conductor 19. This is because of the fact, as has already been hereinbefore set forth, that the contact bridging member 43 of the first thermal retarder switch will be in engagement with the fixed contact members 45 and. 41, if the thermal retarder switch unit is subject to cold water. 9

Heating coil 69 will also be energized through a circuit traceable as follows: from supply circuit conductor 1! through engaged'contact arms' 13 and i5, through conductors 8| 9|, and 93, through heating coil 69, through conductor 95, through engaged contact arms 35 and 33, and

then through conductor 85 to the second supply.

circuit conductor 19.

Under normal operating conditions, energize,- tion of heater 2! through the. hereinbefore described circuit will continue for a length of time not to exceed two or three hours, depending upon the size of the tank as well as the heating capacity of electric heater 2|. When sulficien't water has been heated to a temperature on the order of 150 F, to afiect the thermal retarder switch unit, the

first thermal switch, including particularly bi-'- metal bars 5| and 5|, will be opened with a snap action, so that energization of the heater 2| will be discontinued after say two hours;

Energization of heater 65 will continue, and,

if it will require four hours to cause temperature rise of bimetal bars and 59 to a value.suffi-- tacts and '53 with contactbridging member 51,.

through a part of conductor 83, through conductor 85 and heater 2!, through conductor 81, then through engaged contact arms 35 and 33, and then through conductor 89 to the second supply circuit conductor 19.

Energization of heater 2| through the last above described circuit will continue until substantially all of the Water in the tank is hot, when the lower thermally-actuable switch 25 will open because of being subject to hot water, with the result that both heater 2| and heatin coil 69 will be deenergized. If it would require say three hours to heat up the rest of the water in the tank to a temperature of 150 F. within the offpeak period, the above described deenergization of heater 2| will be efiected.

If, however, because of a demand for hot water in the late night hours, say from 4 to 5 or 6 oclock a. m., some of the hot water is withdrawn, energization of heater 2| will be continued even after opening of the time-controlled switch H through a circuit substantially as follows: from supply circuit conductor 11 through conductor 91, through contacts 6] and 63 and bridging member 51, through a part of conductor 83, through conductor B5, heater 2|, conductor 81, through engaged contact arms and 33, and then through conductor 89 to the second supply circuit conductor 19. Thus, if because of unusual and unexpected calls for hot water, less than all of the water in the tank is hot at the time of opening of the time-controlled switch H at 6 oclock a. m., energization of the heater 2| will continue beyond the end of the oil-peak period, and the heater 2| will be deenergized by the lower thermally-actuable heater control switch 25, as has been hereinbefore described.

The thermal retarder disclosed in this application and the control system, including the thermal retarder heater control switch unit, are therefore effective to cause immediate energization of an electric heater of a domestic hot water tank upon closure of a time-controlled switch at the start of an off-peak period, and is also effective to cause energization of the electric heater with a predetermined time delay period after closure of the time-controlled switch in accordance with whether the thermal retarder switch is subject to cold water or to hot water at the time of closure of the time-controlled switch. The system is further effective to continue energization of the heater 2| beyond the opening of the timecontrolled switch in case the lower thermallyactuable heater control switch is subject to cold water at the time of opening of the time-controlled switch.

Various modifications may be made in the system embodying my invention without departin from the spirit and scope thereof, and all such modifications coming clearly within the scope of the appended claims shall be considered as covered thereby.

I claim as my invention:

1. A control system for a domestic hot water tank having an electric heater, comprising a lower thermally-actuable heater control switch mounted in heat-receiving relation on a tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during oiT-peak periods and a thermal retarder heater control switch unit adapted to be mounted in heat-receiving relation on a tank intermediate the ends thereof and consisting of a first snap-acting thermal switch having two fixed contacts and an open and a closed position, a second snap-acting normally open thermal switch having three fixed contacts and adapted to be moved into closed position when its temperature has reached a predetermined high value, a heating coil for said second switch for heating it to said predetermined high value and electric connections between said heater and said switches to cause immediate energization of said heater, through said lower switch, said time-controlled switch and the first switch of said thermal retarder switch unit after closure of said time-controlled switch in case said thermal retarder switch unit is subject to cold water at that time, the energization through said circuit continuing until the thermal retarder switch unit is subject to hot water, the energization of said heater bein thereafter continued through said lower thermal switch and the second switch of said thermal retarder unit until terminated by said lower thermal switch when substantially all of the water in the tank is hot.

2. A control system for a domestic hot water tank having an electric heater, comprising a lower thermally-actuable heater control switch mounted in heat-receiving relation on a tank adjacent to the lower end thereof and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during off-peak periods and a thermal retarder heater control switch unit adapted to be mounted in heat-receiving relation on a tank intermediate the ends thereof and consisting of a first snap-acting thermal switch having two fixed contacts and an open and a closed position, a second snap-acting normally open thermal switch having three fixed contact and adapted to be moved into closed position when its temperature has reached a predetermined high value, a heating coil for said second switch for heating it to said predetermined high value and electric connections between said heater and said switches to cause energization of said heater through said lower switch, said time-controlled switch and the second switch of said thermal retarder unit after a predetermined time delay period after closure of said time-controlled switch in case the thermal retarder unit is subject to hot water and the lower switch is subject to cold water at that time, the energization continuing through said lower switch and said second switch of the thermal retarder unit if lesS than all of the water in the tank is hot when the time-controlled switch is opened until the heater is deen ergized by opening of the lower thermally-actuable switch when substantially all of the water in the tank is hot.

3. A control system for a domestic hot water tank having an electric heater, comprising a lower thermally-actuable switch adapted to be mounted in heat-receiving relation on a tank at the lower end portion and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during offpeak periods and a thermal retarder heater control switch unit adapted to be mounted on a tank intermediate the ends thereof and consistin of a first snap-acting thermal switch having two fixed contacts and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot waterm the tank, a secondsnap-acting switch having three fixed contacts andr'adapted to be'in open position when subject to cold and to" hot water in the tank and to be in closed position when subject to an appreciably higher temperature, a'heating coil for said second switch for heating it to-said appreciably higher temperature, the energization of said heating coil being controlled jointly by said lower thermally-actuable and said time-controlled switches and electric connections between said heater and said switch to selectively cause immediate energization of said heater upon closure of said timecontrolled switch in case said thermal retarder unit is subject to cold water in the tank at that time and to cause energization of saidheater a predetermined time period after closure of said time-controlled'switch in case said thermal retarder switch is subject to hot Water in the tank at that time.

4. A control system for a domestic hot water tank having an electric heater, comprisin a lower thermally-actuable switch adapted to be mounted in heat-receiving relation on a tank at the lower end portion and adapted to be in closed position when subject to cold water in the tank and to be in open position when subject to hot water in the tank, a time-controlled switch adapted to be in closed position during ofi-peak periods and a thermal retarder heater control switch unit adapted to be mounted on a tank intermediate the ends thereof and consisting of a first snap-acting thermal'switch having-two fixed contacts and adapted'to'be in. closed'position when subject to cold water in thetank and to be in open position when subject to hot water in the tank, a second snap-acting switchhaw ing three'fixed contacts and adapted to be in open position when subject to cold and to hot water in the tank and to be in closed position when subject to an appreciably higher temperature, a heating coil for said second switch for heating it to said appreciably higher tempera ture, the energization of said heating coil being controlled jointly by said lower thermally-actu-- able and said time-controlled switches and electric connections between said heater and said switch to selectively cause immediate energization of said'heater upon closure of said timecontrolled switch in case said thermal retarder unit is subject to cold' water in the tank at that time and to cause energization of said heater a predetermined time period after closure of said time-controlled switch in case said thermal retarder switch is subject to hot water in the" tank at that time, the energization in either case continuing through said lower switch and the second switch of the thermal retarderunituntil interrupted by said lower switch when sub-- stantially all of the water in the tank is hot if less than all of the water in the tank is hot when the time-controlled switch is opened.

CLARK M; OSTERHELD. 

